The production of printed circuits using a variety of resists is described in "Printed Circuits Handbook" edited by Clyde F. Coombs, Second Edition, published by McGraw-Hill, Inc., 1979. Chapter 6 of this publication describes the use of both negative-working and positive-working photoresists in the preparation of printed circuits. In particular, section 14 of chapter 6 discusses conventional positive-working liquid photoresists and section 16 discusses conventional coating methods applying such photoresists to printed circuit substrates. Likewise, the production of printed circuits using photoresists is described in "Photoresist Materials And Processes" by W. S. DeForest published by McGraw-Hill Book Company, 1975. Namely, Chapter 5 of this publication discusses conventional positive resists and the processes of their use in manufacturing printed circuits.
U.S. Pat. No. B1 4,193,797 discloses a dry film process for forming a photoresist comprising applying to a surface of a solid unexposed photosensitive layer of thermoplastic photosoluble or photodesensitizable material, the other surface being releasedly adhered to a film support, exposing the layer to actinic radiation, and removing the film support, and then washing away exposed areas of the layer to uncover areas of the underlying surface. The uncovered areas of the underlying surface can be etched, plated or otherwise modified. The photoactive materials disclosed are photosoluble o-quinonediazides and photodesensitizable bis-diazonium salt compositions.
An electrocoating process is disclosed in U.S. Pat. No. 4,673,458 wherein a positive working photoresist is applied to a printed circuit substrate by electrodeposition with an anionic or cationic electrodeposition bath of quinonediazide sulfonic ester bearing acrylic copolymer. An anionic, positive working photosensitive resin composition is disclosed which is a copolymer having a neutralized, acidic component and an o-quinonediazide ester component. The neutralized polymer obtained is dispersed into water.
In U.S. Pat. No. 3,779,778, novel photosolubilizable compositions are disclosed that comprise 1) a water-insoluble compound containing one or more acid-degradable groups, and 2), a photoinitiator comprising a photolyzable acid progenitor. The useful water-insoluble compounds can contain one or more acid-degradable linkage which can be formed by the nucleophilic reaction of phenols, N-alkyl arylsulfonamides, or certain secondary amines with alkyl vinyl ethers, e.g., methyl vinyl ether, ethyl vinyl ether or a dihydropyran.
J. E. Kearns et al., J. Macromol. Sco.-Chem., A8(4), pp. 673-685 (1974) describe the preparation and deesterification of a number of polymers and copolymers of unsaturated tetrahydropyranyl esters. The utility of dihydropyran as a protecting group in the preparation of polymers containing other groups susceptible to normal hydrolysis conditions is ascribed to the mild conditions required to remove the tetrahydropyranyl group from these esters. In U.S. Pat. No. 4,491,628, resists sensitive to UV, electron beam and x-ray radiation with positive or negative tone upon proper choice of a developer are formulated from a polymer having a recurrent pendant groups such as tert-butyl ester or tert-butyl carbonate groups that undergo efficient acidolysis with concomitant changes in polarity (solubility) together with a photoinitiator which generates acid upon radiolysis. A sensitizer component that alters wavelength sensitivity of the composition may also be added. The preferred acid labile pendant groups are tert-butyl esters of carboxylic acids and tert-butyl carbonates of phenols. It is understood that a wide range of acid labile groups are operative in the invention including trityl, benzyl, benzhydryl modifications as well as others well known in the art.
European Patent Application 0 264 908 discloses resists comprised of at least one polymer, copolymer, or terpolymer having recurrent acid labile groups pendant to the polymer backbone wherein the improvement comprises: selecting a substituent side chain on said acid labile groups which is capable of forming secondary carbonium ion intermediates and having an available proton adjacent to the carbonium ion formed during cleavage. The autodecomposition temperature of the polymer comprising the photoresist is increased to a temperature greater than about 160.degree. C., by selecting substituent side chains on the acid labile group which exhibit a less stable intermediate carbonium ion than the t-butyl ion.
Canadian Patent No. 672,947 discloses novel coating compositions comprising, essentially, a tetrahydropyranyl ester of a linear copolymer of an .alpha.,.beta.- ethylenically unsaturated carboxylic acid, a glycidyl ester of such an acid and at least one other ethylenically unsaturated monomer free of groups reactive with epoxide rings and carboxylic acid groups, which compositions when applied and heated are converted into hard thermoset, solvent resistant films via the crosslinking reaction of the carboxylic acid and epoxide groups.
Although there are a number of positive working photoresist systems based on polymers with acid labile groups and acid generating photosensitive initiators, such systems typically have low photospeed and have limited processing latitude in wholly aqueous solutions in the absence of organic solvent additives. There is a need in the industry for higher photospeed and all aqueous processing in such systems without affecting processing latitude.